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GARNET & SPINEL (Spinel (Characteristics
Singly refractive &…
GARNET & SPINEL
Green Garnet
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Tsavorite
Large tsavorite rough is extremely rare, there’s a huge increase in value between small & large fashioned stones.
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- Trace Element: Vanadium
- Finest Quality: vivid green, with medium to medium-dark tone.
- An effective & less-expensive emerald alternative
Two Major cons to be as a commercial gem:
- the softest of gem garnet
- size is usually small than 3 carats
Source: Tsavorite is mined mostly in East Africa
- Small, calibrated gem cut in Thailand, India &
Si Lanka
- Large, expensive gem cut in Germany
Demantoid
- The transparent green variety of Andradie
- Trace Element: Chromium & Iron
Source:
- Demantoid comes mostly from sources in Russia & Africa.
- Inconsistent supply and continuing demand for demantoid keep prices high.
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Horsetail inclusions can increase demantoid’s value, cutters strive to display them.
“topazolite.” - Attractive, pure yellow andradite
Orange Garnet
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SPESSARTINE
Color Range: Pale yellowish orange through bright orange to a dark brownish red.
The most favored color is a vivid “aurora red
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Spessartine is the most valuable orange garnet, and large, fine-quality stones sell at a premium.
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MALAYA
A pinkish to reddish orange garnet, in the 1960s, while mining for rhodolite in Tanzania’s Umba River Valley
A mixture of pyrope and spessartine, with a small amount of almandine
Trace amounts of iron and manganese cause malaya garnet’s reddish orange “peach” to “cinnamon” brown colors.
HESSONITE
- The transparent orange to cinnamon-colored variety of the grossular species.
- Not much mainstream present
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Red Garnet
Most red garnets, including the popular rhodolite, are mixtures of pyrope and almandine.
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PYROPE & ALMANDINE
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Pyropes
- Stone from Arizona and Utah were marketed as “anthill” garnets.
- Trace Element - Iron --> The color will not be as vibrant as ruby (chromium as the trace element)
Almandine
- The most widespread garnet & sources are usually metamorphic rocks like schist.
- "Hollowback: A cabochon with a curved, undercut bottom, designed to lighten the tone of the gem material.
Most common & widespread gem,
found in metamorphic rocks
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Phenomenal Garnet
Color-change Garnets
- Usually pyrope- spessartine mixtures with vanadium as a coloring agent.
- Blue to bluish green hue in daylight or fluorescent light, & Purple to purple-red in incandescent light.
Star Garnets
- Not as rare as color-change gargents
- Usually almandine or rhodolite, star garnets are filled with rutile silk needles
- Sources: India, Sri Lanka, & the US state of Idaho
Spinel
Characteristics
- Singly refractive & lacks pleochroism
- Well-formed crystals are fairly common
- Color Range: Orange to intense “stoplight” red, vibrant pink, and all shades between purple, blue, and violet through to bluish green.
Trace Element
- Chromium --> Intense red or pink
- Higher the chromium content, the stronger the red hue.
- Mix of Iron & Chromium --> orange & purple
- Iron -->Violet or grayish violet of low saturation
- Cobalt & Iron --> vivide blue, Cobalt spinel (RARE)
Quality
- Red is the most rare and valuable spinel hue, followed by cobalt spinal, the by hot pink & vivid orange
- Finest Quality: Pure red to slightly purplish red hues of medium to medium-dark tone
Source & Market
- Historical sources: Sri Lanka & Afghanistan, the Pamir Mountains in the former Soviet republic of Tajikistan in Central Asia produce large, fine spinel crystals
- Spinel forms in the same metamorphic rocks as corundum, and both gem species are often found in the same alluvial deposits.
Many historically important red gems,
long identified as ruby, were recognized
as spinel in the 1800s.
Synthetic
- Spinel is rare and synthetic spinel is common
- Has approximately the same chemical composition & crystal structure as natural spinel
Both Garnet & Spinel
- Rarely treated
- Effective alternative for costly colored stones
- Singly Refractive, eliminating the need for cutters to consider pleochroism.
Classifying Garnets
- Garnets the same crystal structure but slightly different chemical composition.
- Most common habit is the dodecahedron
- Many garnets are mixtures of two or more garnet species.
- Isomorphous replacement - Substitution of one chemical element for another in the crystal structure of a mineral.
Gemologists classify garnets by their chemistry and their properties, but many dealers sell garnets on the basis of color or origin.
- Pyrope and almandine range in color from purple to orangy red.
- Spessartine range from oranges and yellows,
- Andradite comes in yellow and yellowish green.
- Grossular has the widest color range, from colorless through yellow to reddish orange and orangy red, to a strong vibrant green.
African & Mozambique
- dark toned orange-red to brownish red pyrope-almandine garnets